Molecular weights and associating properties of fragments D and E of fibrinogen. The work started last year on the characterization of isolated D and E fragments will be continued. Molecular weights of these fragments obtained from bovine or human fibrinogen, with either trypsin or plasmin, will be determined by sedimentation equilibrium. It was found in these experiments that homologous fragments show appreciable association. The associating properties also will be investigated using the sedimentation equilibrium method.